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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for5VDC Operation 



Make] Projects 

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Got Wireless? Modify a Simple 



12VDC Wireless Remote Control 



for 5VDC Operation 

Written By: Kevin Fodor 



TOOLS: 



Desoldering Braid (1) 
Desoldering Bulb (1) 
PanaVise(l) 
Soldering iron (1) 



PARTS: 



Hookup wire. 22 AWG(1) 
• Songle SRD-05VDC-SL-C 5VDC Relay 

in 

optional, needed only if you intend to still 
use a relay as your output control 

RF Remote Control Transceiver and 

Receiver Pair (1) 

Various Manufacturers and (eBay) 



SUMMARY 

Adding a remote control switch to nearly any project is easy with these small keyfob-based 
RC relays. They are very inexpensive (<$20) and offer such options as MOMENTARY and 
TOGGLE operation as well as multiple relay channels to control. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 

However, from what I found, these units require 12VDC to operate properly. This article 
explains how to convert one to use only 5VDC. 

Additionally, a further mod converts this unit to provide a simple non-mechanical logic level, 
+5V/0v signal to use as an input to a micro-controller input or other circuit. This allows 
anyone to add a remote control switch capability to nearly any project, even if they don't 
need to control big loads through a relay. 

In this short project I am going to explain the basics of these wireless control devices, 
explain which sections need to be hacked (changed) and finally how to test the 
modifications. 



Step 1 — Overview 





NO = Normally Open 
NC= Normally Closed 



NO- 

c- 

NC- 




k-DC/12V- 



• Shown here is a typical unit you will find on eBay and other discount online outlets. It 
basically involves both a transmitter (keyfob) and receiver. The transmitter is typically a 
single-button keyfob but depending on the model purchased it may have more buttons and 
thus more channels. 

• The receiver is made up of two parts; the RF front end and the decoder. Both are 
packaged together in the same enclosure. 

• Both boards are compactly mounted in a small plastic box which makes it incredibly 
convenient to include and isolate within your own projects. Or you can remove the plastic 
enclosure altogether. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 2 — Initial Checkout 




• Before making any modifications it is probably best to verify that the unit works as 
expected. The unit here is a 12VDC operated version which acts as a remote 
MOMENTARY switch. The relay used to control a load has Normally-Open (NO) and 
Normally-Closed (NC) contacts. 

• Try connecting a simple load (a lamp) to the relay contacts and see that when the 
transmitter button is pressed the light turns on. 







Step 3 — Identify the Parts 




• Now we need to hack the module 
so that it can operate from 5VDC 
rather than 12VDC. But first let's 
identify the parts involved. 

• Pull out the receiver PCB from the 
plastic case and place it into a 
vise. 

• Locate the 12VDC relay and 78L05 
voltage regulator; both of which we 
will be removing. 

• On this board the voltage regulator 
is labeled as Q1 and will be in a 3- 
pin TO-92 package. 

• The relay is the big blue 5-pin 
object in the center. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for5VDC Operation 



Step 4 — De-Solder the Relay 







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• Flip the PCB over and locate the 5 
pins of the 12VDC relay. 

• There are 5 pins on this 
relay that must be de- 
soldered. The blue markers 
indicate where the relay coil pins 
are. The red marks indicate the 
relay contact points. 

• Heat each of the pins and use a 
solder bulb and wick to clean out 
all the solder holding the part in 
place. 

• Gently pry the part off the 
PCB carefully. 



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Step 5 — Inspect Your Work 




Shown here is the PC board with the de-soldered relay removed. Make sure the holes are 
completely cleaned of solder. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 6 — Remove the Voltage Regulator (Ql) 




• Now locate the 78L05 voltage regulator. This part is labeled Q1 and shown in the photo 
with a red rectangle. 

• Desolder using a desoldering bulb and wick. Remove solder from all 3 pins of the TO-92 
package. 

• Gently remove the regulator. If you have trouble you can cut the leads. Just be sure 
to keep the PCB traces intact and not apply too much heat. 



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Step 7 — Short the Voltage Regulator Pins 





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• Insert a jumper wire between pin 1 
and pin 3 of the 78L05. This will 
effectively take the input voltage 
and provide it directly to the output. 
The middle pin is already 
connected to ground. 

• Be careful choosing a new 
5VDC supply for this circuit 
as it now must be a regulated 
5VDC supply. There is no longer 
any on-board voltage regulation. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 8 — Remove and Short Reverse Voltage Protection Diode. 




• Desolder the 1 N4007 diode located 
above the DC power input terminal 
block. If you don't do this you will 
loose about 1 .OV from your power 
supply (so a 5V input results in 
only 4V to the circuit). 

• Solder a wire between the two 
diode terminals in place where the 
diode was. 

• Again, keep in mind that by 
doing this your module no 
longer has reverse input voltage 
protection... so be careful. 



A 



Step 9 — Project Variations 

• Variation #1 : If you have decided that this receiver needs to be able to continue to control 
a relay to drive the intended load, continue to step #10. 

• Variation #2: If you have decided that this receiver needs to be able to drive a logic control 
signal instead, continue to step #12. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 10 — Project Variation #1: Replace Relay with 5VDC Operating Relay 




• This variation will show you how to 
modify the module so that it 
operates a 5VDC relay in response 
to the transmitter button being 
pushed. 

• Here we show a SONGLE 
SRD095VDC-SL-C 5VDC relay we 
are going to replace the previous 
12V relay with. Notice that the 
footprint is identical. 



Step 11 — Project Variation #1: Install the New Relay 




• Place new 5VDC relay into the same position the 12VDC relay was in. 

• Flip over the PCB and solder it into place. 

• Now proceed to step #14 - Testing. 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 12 — Project Variation #2: Modify to Provide A Logic Signal Output 

• This variation will show you how to 
modify the module so that it 
outputs a logic control signal in 
response to the transmitter button 
being pushed. 

• The photo to the left shows a 
simplified version of the output 
driver for the relay from the RF 
decoder. Since we removed the 
relay I am going to show you how 
to modify this circuit to output a 
logic control signal instead. 

• The PNP transistor (Q2) is used to 
drive the relay. Instead of driving a 
relay we are going to tap off of this 
output. 




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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 13 — Project Variation #2: Circuit Modification 



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RF 

Decoder 



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Control 

Input 






• The photo on the left shows that we 
need a pull-up resistor from Q2's 
collector pin to the supply voltage. 
This resistor (R) goes in place 
where the relay coil used to be. 

• The collector pin from the S8050 
PNP transistor now provides us 
with a logic control signal output. 

• When the transmitter button is 
pressed Q2 turns on and the 
control signal is low (OV). 

• When the transmitter is not 
pressed Q2 is off and the control 
signal is high (+5V). 

• If the circuit you are trying 
to drive doesn't already 
have a pull-up resistor, you will 
need one (typically 10k) to pull the 
output high when the transistor is 
not on. But if your circuit already 
has a pull-up you do not need to 
install one. 



Q 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for 5VDC Operation 



Step 14 — Project Variation #2: PCB Modification 




• The photo to the left shows the connections on the PCB we are concerned about. 

• The yellow marker shows the collector side of the relay coil. This is where we will tap off 
our logic control output signal. 

• The blue marker is the relay coil's +V supply (which is now going to be +5V). 

• The orange marker indicates where the Q2 collector pin is located. It is also electrically 
connected to the yellow marker as well. 

• Remember, you do not need a pull-up resistor if your circuit already has one. In my 
case the circuit I intended to drive already had a pull-up resistor, so I did not install 
one here. 



* 



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Got Wireless? Modify a Simple 12VDC Wireless Remote Control for5VDC Operation 



Step 15 — Test 




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• Test your modification, but be sure to only apply 5VDC for now on to the input 
terminals (there is no longer a voltage regulator in place, so be careful). The test 
here is shown with the relay modification, but the same idea is applicable with the logic 
signal modification as well. 

• Attach the output wires and any connectors you need to use. You can use either the 
normally open or normally closed output to test. 

• In this photo you can see I am simply applying a 5VDC power source and I am checking 
that I can remotely operate the small LED using the transmitter. 

• The second photo shows how I wired up my test circuit inside. In this example I tied the 
common connection from the relay to ground and the normally open connection to the 
LED's cathode. The anode of the LED was connected to the +5V supply via a current- 
limiting resistor (~1k). 

• This allowed me to test operation by pressing the button and observe that the LED would 
turn on. 



• By the way, I also added a small Molex connector which I will use to provide power 
to the module and receive the signal from the module. This connector is available at 
Mouser and other electronics suppliers. Click Here For Connector Parts . 



Gr 



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Page 11 of 12 



Got Wireless? Modify a Simple 


12VDC Wireless Remote Control for 5VDC Operation 




Step 16 - 


- Finished! 







1 





• That's it! You're done. Now all you 
need to do is mount it in the 
enclosure of your own project. 

• With certainty this hack voids the 
warranty, which makes it even 
more fun to be able to modify 
something in such a way to use it 
as it was not originally intended. 



After using these instructions you will be able to convert a 12VDC operated wireless switch to a 
5VDC operated one with either a relay or logic level +5V/0V output. 



This document was last generated on 201 2-1 1 -01 08:06:1 4 AM. 



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Page 12 of 12